The soil water retention model developed by Kosugi was modified to be compatible with Mualem's model in order to derive an analytical expression for the relative hydraulic conductivity Kr. The modified water retention model is to be derived by applying a lognormal distribution law to the soil pore radius distribution function. Parameters of this retention model have physical significance on the water content (θ)– capillary pressure (ψ) curve and are related directly to the statistics of the pore radius distribution. The accuracy of the resulting combined water‐retention‐hydraulic‐conductivity model is verified for observed data sets for six soils. Results showed that the proposed model produces acceptable matches with observed water retention curves and adequate predictions of hydraulic conductivities in five out of six cases. The θ − ψ and Kr− ψ (or Kr − θ) curves generated by this model are generally similar to those generated by van Genuchten's model.

Many models for soil water retention have been proposed. However, most of these models are curve‐fitting equations and do not emphasize the physical significance of their empirical parameters. A new retention model that exhibits increased flexibility was developed by applying three‐parameter lognormal distribution laws to the pore radius distribution function ƒ(r) and to the water capacity function, which was taken to be the pore capillary pressure distribution function ƒ(ψ). This model contains three parameters that are closely related to the statistics of ƒ(ψ): the bubbling pressure ψc, the mode ψ0 of ƒ(ψ) and the standard deviation σ of transformed ƒ(ψ). By comparison of this model with three existing models (the van Genuchten model, the Brooks‐Corey model, and the modified Tani model), it was shown that ψc, ψ0, and σ are all essential for a general retention model.

No abstract

Abstract:Since the 1980s, several field studies of pipeflow hydrology have been conducted in forested, steep headwater catchments. However, adequate information is lacking with regard to questions as to how representative these previous studies are and how widespread the phenomena might be. Thus, the aim of this study is to review some studies of pipeflow hydrology on forested steep hillslopes. Several points were clarified. (1) The maximum discharge of pipeflow was mainly determined by the soil pipe diameter. When the condition of both the soil pipe diameter and the slope gradient in forest soil were similar to those in peaty podzol, the maximum discharge of pipeflow on forest slopes was slighter than that in peaty podzol. (2) Pipeflow was delivered from a variety of sources, and the contributing area of pipeflow extended as the soil layer became wetter. Therefore, the dominant contributor (new water and old water) was varied and the contribution of pipeflow to streamflow increased with the increase of rainfall magnitude. (3) The roles of pipeflow in the storm runoff generation processes demonstrated two roles: the concentration of water and the rapid drainage to downslopes. Thus, soil pipes can increase the peak discharge from the hillslope and decrease the peak lag time of the storm hydrograph, when compared to the unpiped hillslope. (4) The roles of pipeflow on hydrological process suggested that the soil pipes contribute to the slope stability by increasing the rate of soil drainage and limiting the development of perched groundwater conditions. However, if the rate of water concentration to the soil pipe network is in excess of the pipeflow transmission capacity, the cavity of the soil pipe could readily be filled with water during a rain event, increasing pore water pressure in the surrounding matrix. In this case, the soil pipe induced slope instability. (5) Moreover, pipe erosion has significant impact on the runoff characteristics of pipeflow, since pipe erosion contributed to a change in the limited drainage capacity of soil pipe. Thus, pipe erosion plays an important role in shallow landslide initiation.

Abstract. To determine the impact of blood glucose profile, involving fluctuation and excursion of blood glucose levels, on glycated proteins, we evaluated the association among the daily profile of blood glucose, and glycated albumin (GA) and HbA1c levels in patients with type 1 diabetes (n = 93) and type 2 diabetes (n = 75). GA levels were strongly correlated with HbA1c levels in type 1 (r = 0.85, P<0.0001) and type 2 diabetes (r = 0.61, P<0.0001), respectively. HbA1c levels were similar between patients with type 1 and type 2 diabetes, while GA levels were significantly higher in type 1 diabetes. Thus the ratio of GA levels to HbA1c levels was significantly higher in type 1 diabetes than that in type 2 diabetes (3.32 ± 0.36 vs. 2.89 ± 0.44, p<0.001). The degrees of GA levels and HbA1c levels correlated with maximum and mean blood glucose levels in patients with type 1 and type 2 diabetes. Stepwise multivariate analysis revealed that GA levels independently correlated with maximum blood glucose levels in type 1 diabetes (F = 43.34, P<0.001) and type 2 diabetes (F = 41.57, P<0.001). HbA1c levels also independently correlated with maximum blood glucose levels in type 1 diabetes (F = 34.78, P<0.001), as well as being correlated with mean blood glucose levels in type 2 diabetes (F = 11.28, P<0.001). In summary, GA could be a better marker for glycemic control than glycated hemoglobin in diabetic patients, especially for evaluating glycemic excursion, which is considered to be a major cause of diabetic angiopathy.

[1] Recent studies have suggested that bedrock groundwater can exert considerable influence on runoff generation, water chemistry, and the occurrence of landslides in headwater catchments. To clarify water infiltration and redistribution processes between soil and shallow bedrock and their effect on storm and base flow discharge processes in a small headwater catchment underlain by weathered granite, we conducted hydrometric observations using soil and bedrock tensiometers combined with hydrochemical measurements and water budget analyses at three different spatial scales. Results showed that in an unchanneled 0.024-ha headwater catchment, saturated and unsaturated infiltration from soil to bedrock is a dominant hydrological process at the soil-bedrock interface. Annual bedrock infiltration ranged from 35 to 55% of annual precipitation and increased as precipitation increased, suggesting a high level of potential bedrock infiltration, partly explained by the high buffering capacity of the soil layer overlying the bedrock. This physical property of the soil layer was an important factor in controlling the generation of bedrock infiltration and saturated lateral flow over the bedrock. In a 0.086-ha watershed including the unchanneled headwater catchment, exfiltration from the bedrock toward the soil layer composed more than half the annual discharge.

[1] Both scaling effect and connectivity of overland flow were examined in steep hillslopes covered by (1) Japanese cypress (hinoki, Chamecyparis obtusa) plantations with sparse understory vegetation, (2) hinoki plantations with fern understory vegetation, and (3) deciduous forests. Two sizes of plots were installed for monitoring overland flow: small (0.5 Â 2 m) and large hillslope scale (8 Â 24-27 m). For all hillslopes, measurable amounts of overland flow occurred during storms. Runoff coefficients of large plots (0.1-3%) were consistently smaller than those of small plots (20-40%). Estimated runoff flow lengths at the hillslope scale were based on runoff coefficients from small plots and were used to calculate runoff volume from large plots. Then we compared the differences between observed and estimated runoff volumes of large plots. Estimated runoff from large plots was smaller than observed runoff in hinoki slopes with sparse understory vegetation. Greater amounts of observed compared to estimated overland flow suggest that more runoff occurred from hillslopes with sparse understory. In contrast, estimated overland flow was larger than observed runoff from the deciduous forest, implying greater opportunities for infiltration compared to hinoki hillslopes. Comparison of estimated versus observed overland flow for successive 5 min intervals during storms indicates that runoff networks expand upslope during short and intense precipitation periods. Our examination and comparison of storm runoff from small and large plots facilitate better understanding of runoff mechanisms, scaling effects in hillslopes, and connectivity of the overland flow network.

OBJECTIVEThe effect of additional treatment with oral hypoglycemic agents on the progression of atherosclerosis remains unknown in insulin-treated patients with type 2 diabetes mellitus (T2DM). We assessed the effects of sitagliptin, a dipeptidyl peptidase 4 inhibitor, on carotid intima-media thickness (IMT) in T2DM. RESEARCH DESIGN AND METHODSThis prospective, randomized, open-label, blinded end point, multicenter, parallelgroup, comparative study included 282 insulin-treated patients with T2DM free of a history of apparent cardiovascular diseases who were recruited at 12 clinical units and randomly allocated to either the sitagliptin group (n = 142) or the control group (n = 140). The primary outcomes were changes in mean and maximum IMT of the common carotid artery measured by echography at the end of a 104-week treatment period. RESULTSSitagliptin had a more potent glucose-lowering effect compared with the conventional treatment (20.5 6 1.0% vs. 20.2 6 0.9%; P = 0.004), without increasing hypoglycemic episodes or body weight. Changes in the mean and left maximum IMT, but not right maximum IMT, of the common carotid arteries were significantly greater after sitagliptin treatment compared with conventional treatment CONCLUSIONSSitagliptin attenuated the progression of carotid IMT in insulin-treated patients with T2DM free of apparent cardiovascular disease compared with conventional treatment.